1. Field of the Invention
The present invention pertains to a wireless communication system, a wireless access point, a communication control method, and a computer-readable medium storing a communication control program, the system including wireless access points (base station) that communicate with backbone networks only wirelessly and those only through cable.
2. Description of the Related Art
There has been known a mesh network which uses a wireless communication line for a communication path (for example, between access points) up to a connecting point to a backbone network such as a wired Local Area Network (LAN). In the mesh network, an access point (a base station) receives a packet sent from a user. The packet is then relayed to an upper-level network (backhaul).
The wireless communication line adopted as the communication path up to the point connecting to a backbone communication line occupies a frequency band, which is in general shared among a plurality of access points (to be referred to as wireless AP hereinbelow) connected via a wireless communication to the backbone communication line. The user traffic of packets transmitted using wireless communication terminals or stations connected to the respective wireless access points are delivered via the shared wireless communication line to the destinations of the respective packets.
There exists a conventional wireless communication system in which when a station obtains hop count information and cannot directly connect to a wireless access point, an upper-level connection destination, the system selects a second wireless access point having the smallest hop count to thereby connect the station to the wireless access point (see, for example, Japanese Patent Application Laid-Open No. 2001-237764 (document 1)).
In a conventional wireless communication system, there exists an upper-limit value for the frequency band of the wireless communication line employed as the communication path up to the connection point to the backbone communication line. Therefore, the user packets for the stations coupled with the respective wireless access points share the frequency band.
For example, in the example shown in FIG. 1, when a station belonging to a wireless access point 502a transmits a packet to a transmission destination address “192.168.1.0/24”, the packet transmitted from the station is wirelessly relayed twice from the access point 502a to be transferred to a wired access point 501b which is in charge of the address “192.168.1.0/24”.
The packet is then sent from the wired access point 501b via a wired communication path to the destination.
There also exists a conventional system in which a mobile node measures at least one of the hop count and the communication delay time between the node and a home agent. In the system, if the communication delay time is equal to or more than a predetermined value, the agent to which the mobile node belongs is changed to another agent for which the communication delay time is equal to or less than the predetermined value. Otherwise, if the hop count is equal to or more than a predetermined value, the agent to which the mobile node belongs is altered to another agent for which the hop count is equal to or less than the predetermined value (see, for example, Japanese Patent Application Laid-Open No. 2004-7578 (document 2)).
Referring now to FIG. 2, description will be given of problems in the configuration of the conventional system that changes, according to the hop count, the agent to which the node belongs.
As shown in the example of FIG. 2, when a station belonging to a wireless access point 502a sends a packet to the address “192.168.1.0/24”, a hop count becomes smaller if the station belongs to a wired access point 501b in charge of the address “192.168.1.0/24”. Therefore, the station first changes an access point to the wired access point 501b and then delivers a data frame to the destination address (communication path A).
Description will now be given of a case in which the destination address is altered to “10.1.1.0/24” as a result of an operation in which, for example, the application to be used by the station is changed. In this situation, it is required to relay three times the data along a route which begins at the wired access point 501b and passes through the wireless AP 502b, the wireless AP 502a, and the wired AP 501a (communication path B) as shown in the example of FIG. 2.
Next, description will be given of problems associated with the conventional techniques.
First, in the wireless communication system of the prior art described by referring to FIG. 1, if the station is apart from the packet destination in the network, the number of relays, i.e., the hop count required to send the packet to an access point (wired AP) that is coupled only by a wired line with the backbone communication line becomes greater. In this case, the band is wasted.
In the technique described in document 1, the station needs processing to attain the hop count information. Also, when a wireless access point wirelessly connected to the backbone communication line receives a packet from a client terminal, the hop count is not zero. Therefore, the traffic is not reduced depending on cases.
In the technique described in document 2, the access point to which the station belongs is changed to reduce the communication delay time or the hop count to a value equal to or less than the predetermined value. Therefore, each time the transmission destination from the mobile node is altered, it is required to change the access point to which the station belongs.
In the example shown in FIG. 2, the problem can be avoided by changing the wireless access point to which the station belongs to the wireless access point 501a in charge of the destination address “10.1.1.0/24”. However, for this purpose, each time the transmission destination address is changed by an application, it is required to switch access points to which the station belongs.
This possibly leads to the problems as below.
(1) The processing to change the access point takes a long period of time and brings about a non-communication state or the disconnection of sessions, thereby hindering the communication in some cases.
(2) When an authentication server is employed to conduct authentication, encryption key information is to be communicated as a new access point is chosen. This may increase the traffic.
(3) The band must be newly saved after a new access point is chosen. Therefore, if another station issues a request for belonging to an access point while the access point change processing is under way, a new access point could not be appointed.